11.
|
Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in:
|
A.
|
6 hours
|
B.
|
|
C.
|
7 hours
|
D.
|
|
|
Answer: Option C
Explanation:
(A + B)'s 1 hour's work =
|
|
1
|
+
|
1
|
|
=
|
9
|
=
|
3
|
.
|
12
|
15
|
60
|
20
|
(A + C)'s hour's work =
|
|
1
|
+
|
1
|
|
=
|
8
|
=
|
2
|
.
|
12
|
20
|
60
|
15
|
Part filled in 2 hrs =
|
|
3
|
+
|
2
|
|
=
|
17
|
.
|
20
|
15
|
60
|
Part filled in 6 hrs =
|
|
3 x
|
17
|
|
=
|
17
|
.
|
60
|
20
|
Remaining part =
|
|
1 -
|
17
|
|
=
|
3
|
.
|
20
|
20
|
Now, it is the turn of A and B and
|
3
|
part is filled by A and B in 1 hour.
|
20
|
Total time taken to fill the tank = (6 + 1) hrs = 7 hrs.
